Diagnosis, ECG, Healthcare, Heart Health, Heart Monitoring

Reading the ECG Heart Monitor Lines – the Complete Guide

How to read ECG Heart Monitor Lines

An electrocardiogram (ECG or EKG) is a device that records the electrical signal from the heart and is used as one of several diagnostic tests for cardiovascular conditions. Doctors also order ECG heart monitor line to evaluate a person’s heart function to determine whether their heart disease has aggravated or not.

After all, ECG is a representation of the heart muscle’s electrical activity, and it changes with time.

Although it seems complicated, reading the ECG heart monitor line is quite simple, and we’re going to guide you through it in this post.

Thorough Patient Evaluation

Patients usually need to answer various questions before a doctor orders an ECG to diagnose a certain condition or to determine whether it’s worsened. The primary intent behind these questions isn’t to be intrusive, but to learn more about the patient and their general health status, and lifestyle. Reading the ECG analysis isn’t enough on its own. What’s normal for an athlete may not be good for someone whose lifestyle is sedentary. 

Understand Normal Values

Normal heart rhythm contains:

  • P wave – this heart wave represents depolarization of the left and right atria and corresponds to atrial contraction. The absence of P waves and the presence of irregular rhythm indicate atrial fibrillation.
  • QRS – represents the electrical impulse as it spreads through ventricles and indicates ventricular depolarization; it starts before ventricular contraction. Pay attention to the width, height, and morphology of the QRS complex. The width can be narrow (<0.12 seconds) or broad (>0.12 seconds), while the height can be small or tall. Morphology is assessed by focusing on individual waves of the complex to look for isolated waves or any progression in their representation.
  • T wave – represents the repolarization of ventricles. T waves are considered tall if they are >5mm in the limb leads and >10mm in the chest leads. Tall T waves are associated with hyperkalemia (elevated levels of potassium) and hyperacute STEMI.

Proper ECG interpretation also depends on understanding the following:

  • Amplitude – measures the voltage of the heartbeat, expressed in the vertical dimension, measured in millivolts (mV) e.g., 1mV is represented by a deflection of 10mm.
  • Deflection – the average direction of electrical travel. A wave of depolarization traveling to a positive electrode results in positive deflection. Whereas a wave depolarization traveling away from the positive electrode shows negative deflection.
  • Duration – measured by squares going horizontal.

When it comes to heart rate itself, the following rules apply:

  • Normal – 60-100 bpm (beats per minute);
  • Tachycardia – >100 bpm;
  • Bradycardia – <60 bpm.

Follow Simple Rules 

Reading ECG waves labeled on the paper, and all the values is not as difficult as it seems. This simple 12-lead ECG protocol can help you out:

  • Determine the heart rate;
  • Detect whether the heart rhythm is regular or irregular e.g., you can use a piece of paper and a pencil to track P waves and QRS complexes to see if they match or have gaps. Irregular rhythm is indicated by a recurrent pattern of irregularity (regularly irregular), or it is completely disorganized (irregularly irregular).
  • Determine if the heart rhythm is fast or slow.
  • Examine ST segments for any elevation or depression (you can use a pencil and paper for this as well). The ST segment is the part of ECG from the end of the QRS complex to the beginning of the T wave; it remains isoelectric. Elevation or depression of ST segment indicates cardiac pathology.

Determine the Cardiac Axis

The cardiac axis represents the overall direction of the electrical spread within a person’s heart. In healthy people, the axis spreads from 11 o’clock to 5 o’clock. For this purpose, leads I, II, and III are used.

The normal cardiac axis is indicated by lead II having the most positive deflection.

Right axis deviation occurs when lead III has the most positive deflection and lead I is negative. On the other hand, the left axis deviation is represented by lead I as the most positive deflection. While leads II and III are negative.

Analyze PR Interval

The PR interval is measured in units of time. It represents the time from the onset of the P wave to the start of the QRS complex. The normal PR interval value should be between 120 and 200 ms (3 to 5 small squares).

When analyzing the PR interval, you need to bear in mind the following values:

  • A prolonged PR interval (>0.2 seconds) – indicates the presence of atrioventricular delay (AV block).
  • Shortened PR interval – means that the P wave is originating somewhere closer to the AV node. It can also indicate that the atrial impulse is reaching a ventricle through a faster shortcut. Rather than conducting slowly across the atrial wall.


Reading the ECG heart monitor line is easier than it looks. It’s important to learn what waves and values represent.

Then, you can determine if the results indicate normal heart function or potential disruptions.

Besides these values, it’s also important to assess lifestyle, daily habits, medical history, and other factors. In order to help doctors paint a more detailed picture.

Speaking of help, personal ECG devices are beneficial tools for you and your doctor. These solutions allow you to measure your ECG on your own and see results on your phone outside a medical institution. Personal ECG increases the chances to detect any abnormalities and act timely. In addition, part of them monitors other factors that impact your ECG. Thereby, letting you understand the causes and build a more effective treatment plan.

Having a piece of paper and pen to track heart monitor line waves and values for potential depressions and elevations or other irregularities is a practical way to understand what ECG results mean.

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1 Comment

  1. Usually people want to know what a normal heart line looks like on a monitor including numbers. Then ad normal picture and what that means including numbers. I’m trying to understand what normal is with numbers and what the heart is doing. Then ad normal picture and what is happening to the heart including numbers. Please explain.

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